1. Field of the Invention
The present invention relates to a linear motion guide unit with lubricating means, which is applicable to industrial robots, semiconductor manufacturing apparatus, machine tools and the like to lubricate the relatively sliding parts and components.
2. Description of the Prior Art
The linear motion guide units have been conventionally used incorporated in the parts or components for reciprocating motion in fields as diverse as the industrial robots, semiconductor manufacturing machines, inspection instruments, machine tools or the like, and further developed to answer the needs for precision, high-speed, miniaturization or the like. The recently remarkable development in mechatronics technology extensively requires linear motion guide units that may meet with needs of maintenance-free, especially, the self-lubrication of long service life on its relatively movable sliding areas, along with miniaturization, high precision and high speed in operation.
FIG. 16 shows an example of prior linear motion guide units.
The linear motion guide unit in FIG. 16 is primarily comprised of a track rail 2 and a sliding element, or a slider 1, riding the track rail 2 astride for sliding movement. The track rail 2 is formed on lengthwise side surfaces 3 thereof with raceway grooves 4. The slider 1 may move on the track rail 2 by virtue of rolling elements running through the raceway groove 4. The track rail 1 has on lengthwise upper surface 14 thereof openings 13 spaced from each other. The track rail 2 is fixed to a mounting base 20 such as beds, working tables or the like by screwing bolts through the openings 13 of the track rail 2 and matching openings in the mounting base 20. The slider 1 has a casing 5 movable with respect to the track rail 2, and end caps 6 attached to the opposing ends of the casing 5. Provided on the upper surface of the casing 5 are openings 19 for fixture to mount other appliances, chucks, parts or the like on the slider 1.
Both the casing 5 and end caps 6 are made on the lower surfaces thereof with recesses 10, where the casing 5 and end caps 6 may sit astride the track rail 2 for free movement. The recesses 10 are each made with raceway grooves 9 in opposition to the raceway grooves 4 on the track rail 2. The rolling elements 7 contained in the casing 5 run through load areas of raceways defined between the confronting raceway grooves 4 and 9. Retainer bands 18 are provided in the casing 5 so as to embrace the rolling elements 7 to thereby prevent the rolling elements 7 from falling out of the casing 5. Bottom seals 8 are attached to the lower surfaces of the slider 1 to close clearances between the track rail 2 and the slider 1.
The end caps 6 are provided therein with members for scooping up the rolling elements 7 from the raceway grooves 4 on the track rail 2, and turnarounds for circulating the rolling elements 7. Mounted on the end caps 6 are end seals 17 for ensuring the sealing performance between the track rail 2 and the lengthwise opposing ends of slider 1. The end caps 6 are fixed to the opposing ends of the casing 5 by means of bolts 25, which are screwed into their matching holes. The raceways defined by the confronting raceway grooves 4, 9, turnarounds formed in the end caps 6 and return passages 12 formed in parallel with the raceway grooves 9 in the casing 5, in combination, constitute endless-circulating paths for the rolling elements 7. Even though the rolling elements 7 are under loaded condition in the raceways, rolling-contact of the rolling elements 7 with the raceway grooves 4, 9 may help ensure the smooth movement of the slider 1 relative of the track rail 2. Grease nipples 11 are connected to the end caps 6, passing through the end seals 17 to apply lubricant to the confronting raceway grooves 4, 9 where the rolling elements 7 run through.
To lubricate the raceways where the rolling elements 7 run through, grease or lubricating oil is usually employed. In case of grease, it is applied to the raceways through grease nipples 11. In contrast, lubricating oil is supplied to the raceways through pipe joints, which are used substituting for the grease nipples.
Japanese Patent Laid-Open No. 53637/1997, has disclosed a linear motion guide unit having for its object to provide a maintenance-free lubrication system for the raceways, in which a reinforcing plate, lubricant-containing member and side seal, overlapped one on the other, are fixed on the outward surface of an end cap mounted on a casing. The reinforcing plate is of a steel sheet having a substantially inverted U-shape, which is fit to the outward contour of the end cap, but does not come in contact with the track rail. The lubricant-containing member is provided on the inside thereof with convexities, which are formed in adaptation with the cross section of the track rail so as to come in sliding contact with the upper and side surfaces of the track rail. For constant supply of the lubricant from the lubricant-containing member to the raceway grooves, the lubricant-containing member is urged resiliently against the raceway grooves on the track rail by ring members fitted in holes formed in the lubricant-containing member, or resilient members adapted to the lubricant-containing member.
Japanese Patent Laid-Open No. 205534/1998, which is a senior co-pending application, discloses a linear motion guide unit comprising a track rail with raceway grooves and a slider movable along the track rail. The slider is composed of a casing provided with raceway grooves formed confronting the raceway grooves on the track rail, rolling element running through between the confronting raceway grooves, end caps fixed to the opposite ends of the casing, one to each end, lubricating plates affixed on the end surfaces of the end caps, and end seals attached onto the lubricating plates. The lubricating plate is of a sintered resinous component of porous structure and urged against the raceway grooves on the track rail by spring effect of resilient metal casing covering around the peripheries of the lubricating plate.
Moreover, the prior linear motion guide units with lubricating plate of other types have been developed and disclosed in, for example, Japanese Patent Laid-Open Nos. 82507/1999 and 93952/1999, which are senior co-pending applications. In the linear motion guide units cited above, the lubricating plate of the lubricant-containing member is directly urged against the raceway grooves on the track rail and, therefore, the lubricant-containing member moves in sliding engagement with the raceway grooves of the track rail as the slider moves with respect to the track rail. This raises a major problem in which the sliding friction due to the engagement of the lubricant-containing member with the raceway grooves causes much sliding resistance acting on the slider. As a result, it will be understood that the linear motion guide units with the lubricating plate constructed as cited above are unfit for the machines or apparatus to be operated at high speed, where the linear motion guide units incorporated is required to drive their sliders with high travelling speed.
In addition, most linear motion guide units are usually kept against the invasion of debris or dust by means of the end seals covering the end surfaces of the units, which are each composed of a rubber member of, for example, acrylonitrile-butadiene rubbers and a core metal. Nevertheless, the linear motion guide units have been recently employed in fields as diverse as conditions where the lubrication cannot be tolerated, and severe operating conditions, for example, where much debris and dust, chips or the like are apt to occur and adhere to the components or parts. With the environments where the linear motion guide units operate, consequently, the lubricant-containing member in the lubricating plate is susceptible to clogging up caused by the adhered debris so that there is a fear of obstructing the supply of lubricant. Moreover, direct contact of the lubricant-containing member in the lubricating plate with the raceway grooves of the track rail causes a major problem in which much area of sliding contact results in much consumption of lubricant.